1. Field of the Invention
The present invention relates to an amplifier, and more particularly, to a power amplifier. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for enhancing output efficiency.
2. Discussion of the Related Art
Recently, wireless telecommunication services, such as wireless telephones, wireless local area network (LAN), and so on, are being extensively provided throughout the world. More specifically, wireless mobile telecommunication services, such as the European global system for mobile communication (GSM) 900 in 890–915 MHz, the North American advanced mobile phone service (AMPS) 800 in 824–849 MHz, the U.S. personal communication system (PCS) 1900 in 1850–1910 MHz, the Korean PCS 1900 in 1750–1780 MHz, and so on, are being provided.
Especially, recently developed mobile phones are used in diverse color moving images, which are highly power consuming, through wireless internet services, and so assembly parts requiring low power are on demand by mobile phone and communication service providers. Among wireless mobile phones, the power amplifier of a radio frequency (RF) receiver consumes the largest amount of power.
A method for enhancing the power efficiency of the power amplifier is to operate the power amplifier in a high power mode or a low power mode depending upon the outputted power. Herein, the consumed power is reduced in the lower power mode.
In addition, a zero intermediate frequency (IF) conversion circuit or a direct conversion circuit is adopted in the recent mobile communication system, so as to reduce the number of RF receivers and to reduce the time used in mobile phone development.
In the mobile communication system adopting the IF conversion circuit, a power amplifier having a power gain between the high power mode and the low power mode of about 10 decibels (dB) is required. However, the power amplifier generally used in the present technology has a power gain between the high power mode and the low power mode in the range of about 2 to 3 decibels (dB). Accordingly, a power amplifier having a larger gain difference between the high power mode and the low power mode is required and on demand.